JPH0364220B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an investment casting method using a ceramic shell mold.

(Background of the Invention) In an investment casting method using a ceramic shell mold, in order to improve the mechanical properties of a cast product, an appropriate temperature gradient is applied during solidification of the molten metal to cause crystal growth in the direction of this temperature gradient. Sexually coagulated tissue may be obtained. In this case, conventionally, a part of the hot water is cooled with a chiller, and crystals are grown from around the chiller. In addition, the sprue is designed to generate strong turbulence in the hot water flowing into the mold, and the solidification temperature is adjusted to obtain crystals with a fine structure.

However, in the conventional method, when the hot water in the mold is solidified from one part, the hot water remains molten in other parts up to the part that contacts the mold. In other words, as the molten metal solidifies, the molten metal in contact with the inner surface of the mold, which forms the surface of the product, also solidifies. For this reason, there was a problem that cavities appeared on the surface of the product, surface deviation occurred, and pinballs were likely to appear on the product surface, resulting in a poor yield of the product. Another problem was that it took a long time to cool down, resulting in poor productivity.

Therefore, it may be possible to rapidly cool the mold from the outside after pouring the metal. However, ceramic shell molds are heated to a high temperature (approximately 1000℃) and then poured.
If this high-temperature mold is rapidly cooled, the product will be prone to cracking, flattening, and blowholes, which will further reduce product yield and quality.

On the other hand, especially when casting a thin-walled product, it is also required to improve the circulation of hot water in the thin-walled part to increase the product yield.

(Object of the Invention) The present invention has been made in view of the above circumstances, and when investment casting is performed using a ceramic shell mold, there are no cavities or holes on the surface of the cast product.
Defects such as surface deviation and pinholes do not appear, and the internal structure can be made into a unidirectional solidified structure or microstructure with excellent mechanical properties, and productivity is high, and it is especially suitable for thin-walled products. It is an object of the present invention to provide an investment casting method that can improve the flow of hot water to thin-walled parts during casting and increase the yield of products.

(Structure of the Invention) According to the present invention, this object is to increase the thickness of the wall of the runner 68 that communicates the sprue rod portion 64 of the mold 60 with the product portion 66 in an investment casting method using a tree-shaped ceramic shell mold. A constricted part 70 facing the sprue rod part 64 is formed in the runner 68 to increase the heat capacity, and after the entire mold 60 into which the molten metal has been poured is naturally cooled for a while, it is forcibly poured from the outside. An investment casting method characterized by first solidifying the entire inner surface of the mold 60 in contact with the hot water in the product part 66 into a shell shape by rapid cooling, and then sequentially solidifying the inside of the product part 66 and the constricted part 70; This is achieved by

(Example) Figures 1 and 2 are a plan view and a cross-sectional view taken along the line 1, and Figure 3 is a partially sectional side view of the cooling device used in carrying out the present invention. It is.

In these figures, reference numeral 10 denotes a frame fixed to a base, and this frame 10 is composed of four upright legs 12 and four beams 14 connecting the vertices of these legs 12 to each other. Reference numeral 16 denotes a cover, which is made in the shape of a tunnel with an inverted convex cross section, and its lower part is open toward a pair of rails 18, 18 fixed to the base. This cover 16 is suspended from four connecting brackets 20 of the beam 14 of the frame 10. Reverse concave plates 22 are fixed to the front and rear openings of the cover 16. This plate 22 prevents water and steam from scattering to the outside when water is sprayed as described later. Note that FIG. 2 shows the inside of the cover 16 with one of the plates 22 removed. A chimney-shaped exhaust pipe 24 projects from the top of the cover 16.

26 is a water tank, which is attached to the upper part of the frame 10. Water is injected into this water tank 26 from the outside through a pipe 28.
The water level in the tank 6 is always kept substantially constant by a float valve 30. In FIGS. 1 and 2, 32 is a drain pipe for overflow prevention to drain water when the water level in the tank 26 exceeds a specified level, and in FIG. 1, 34 is a drain pipe communicating with the bottom of the tank 26.

36 is an inverted U that crosses the upper part of the inside of the cover 16.
The main pipe is bent into a letter shape, and sub pipes 38, 38 which are long in the longitudinal direction of the tunnel of the cover 16 are connected to both ends of the main pipe 36, and these sub pipes 3
A large number of vertical branch pipes 40 are connected to the pipes 8 and 38. These main pipe 36, sub pipe 38 and branch pipe 40
is a waterway through which water, which is a cooling medium, passes. Further, a large number of nozzles 42 are attached to the main pipe 36 and the branch pipes 40, and these nozzles 42 are used to hold the mold 6 after pouring, which is carried into the cover 16 on a trolley 56 (described later).
It is oriented towards 0.

44 is a water conduit pipe that leads water from the water tank 26 to the main pipe 36. This water conduit 44 includes an electric pressure pump 46 and a valve 4 in order from the water tank 26 side.
8. A pressure gauge 50 is attached. By pressing the switch 52 shown in Figs. 1 and 3, the pressure pump 4 is
6 is turned on for a certain period of time, a certain amount of water is pressurized and guided to the main pipe 36, the sub pipe 38, and the branch pipe 40. Note that the downstream side of the valve 48 communicates with the water tank 26 via a valve 53 and a detour 54 . By changing the opening degree of this valve 53,
The pressure of the pressurized water discharged by the pump 46 can be adjusted.

56 is a cart that moves on the rails 18. A partition wall 58 made of wire mesh is attached to the upper part of this cart 56.
is formed, and a plurality of tree-shaped molds 60 are placed here. This cart 56 is made to have a height and width that allows it to pass under the plate 22 attached to both openings of the cover 16.

FIG. 4 is a sectional view of the tree-shaped ceramic shell mold, and FIG. 5 is a partially enlarged view thereof. In these figures, 62 is the sprue, 64 is the sprue rod, 66 is the product part,
Further, 68 is a runner that communicates the sprue rod portion 64 and the product portion 66, and a constricted portion 70 is formed in this runner 68 so as to face the sprue rod portion 64. In this embodiment, since the runner 68 is short, the runner 68 and the throttle part 70 are almost integrated, but generally the runner 68 is long and a part of the runner 68 has a throttle part. Of course, 70 will be formed.

The tree-shaped mold 60 is made by brazing a wax pattern onto a wax sprue rod, repeatedly dipping this wax pattern tree into a slurry tank and a stucco tank to form a ceramic layer, and then dewaxing and firing. It is made through a process. Therefore, slurry and stucco particles adhere thickly to the walls forming the runner 68, and the heat capacity of the runner 68 as a whole increases. Further, since the wall thickness around the constricted portion 70 provided in the runner 68 is greater than that of other parts of the runner 68 where the constricted portion 70 is not provided, the heat capacity around the constricted portion 70 is further increased.

(Operation) Next, the operation of this embodiment will be explained. The mold 60 made as described above is placed on the trolley 56 with the sprue facing upward.
After being placed in
In the pouring process, molten metal is poured into the hot mold 60. The cart 56 moves on the rails 18 while the hot water remains molten and enters the cover 16 shown in the figure. That is, during this movement, the mold 60 is naturally cooled by the surrounding air. During this temporary natural cooling, the molten metal flows deep into the high-temperature mold 60, and particularly smoothly flows into thin-walled areas.

After that, when the switch 52 is pressed, the pump 46 is operated for a predetermined time, and pressurized water whose pressure is regulated by the valve 53 is sent to the nozzle 42, and the water is turned into a mist and sprayed onto the mold 60. Therefore, the mold 60 is forcibly quenched from the outside. The water removes heat of vaporization from the mold 60 and evaporates, and the steam is discharged to the outside from the exhaust pipe 24.

Since the mold 60 is forcibly quenched from the outside,
As shown by a in FIG. 5, the entire area where the hot water contacts the inner surface of the mold first solidifies into a shell or skin shape. The area near the runner 68 and the constriction part 70 has a large heat capacity and is in contact with the sprue rod part 64 containing a large amount of hot water, so the temperature decreases slowly. In particular, since the constriction section 70 is located at a position facing the sprue rod section 64, solidification of the molten metal is delayed in the vicinity of the constriction section 70.

Therefore, coagulation progresses inward in sequence as shown in a, b, c, and d, resulting in a unidirectionally coagulated structure. In addition, the hot water before solidification in the center of the product section 66 is
8. Since the hot water in the sprue rod 64 and the sprue 62 are in communication, the hot water in the product section 66 is always pressurized by the hot water in the sprue 62 and the sprue rod 64, and the hot water effect can be generated to the end. can. Therefore, defects such as cavities are less likely to occur. In addition, most of the surface layer of the product is formed almost simultaneously by rapid cooling, so even if a cavity were to form inside the product, the cavity would not appear on the product surface, and defects such as pinholes would not appear on the surface. It stops appearing.

In addition, since the molten metal is naturally cooled for a while after pouring, the molten metal flows sufficiently into the mold 60 during this time, and the molten metal flows particularly well in thin-walled products.

(Experimental Example) Next, an experimental example of the present invention will be explained. A ceramic shell mold was made from a tree approximately 40 cm tall, made up of seven shift forks used in passenger car transmissions arranged in three rows, and iron was poured into the mold. Thereafter, water pressurized to about 6 km/cm ² was immediately sprayed from a nozzle for 40 to 80 seconds using the apparatus shown in FIGS. 1 to 3 to rapidly cool the sample. As a result, we have created a product that does not have defects such as cavities, surface sinking, and pinholes that appear on the surface.

In this experimental example, iron was poured, but iron has a lower surface tension than aluminum alloy, so in the conventional method, it was necessary to increase the diameter of the runner 68 and the constriction part 70 in order to prolong the feeder effect. Ta. For this reason, turbulence during pouring was weakened, and crystal refinement was hindered.
However, according to the present invention, since the feeder effect is large, the diameter of the runner 68 and the throttle part 70 can be reduced, and by strengthening the turbulent flow during pouring, it is possible to promote finer crystals.
It is possible to further improve the mechanical properties of the product.

In the above embodiments, pressurized water was used for quenching, but in the present invention, other than water, a refrigerant such as cooling air or liquid nitrogen can also be used. Furthermore, if these refrigerants are sprayed as in the embodiment, the entire mold can be uniformly rapidly cooled, but in the present invention, the mold is immersed in the refrigerant, etc.
Other quenching methods may also be used.

(Effects of the Invention) As described above, the present invention provides the constricted portion 70 in the runner 68 so as to face the sprue rod portion 64, thickens the runner 68 of the mold to increase the heat capacity, and after pouring After being naturally cooled for a while, the entire mold is forcibly cooled down rapidly, and the hot water in the product section 66 is solidified into a shell shape starting from the part that contacts the inner surface of the mold 60. Therefore, the solidification of the runner is slowed down, and the effect of the molten hot water in the sprue rod 64 through the runner 68 can be fully utilized during solidification, making it difficult for surface shrinkage and cavities to occur. This will improve product yield. Furthermore, unidirectional solidification and crystal refinement are possible, which improves the mechanical properties of the product.

Furthermore, since the riser effect occurs for a long time during solidification,
Even if the mold 60 is quenched from the outside, the yield of the product does not decrease, and this forced quenching can shorten the cooling time, improving productivity. Furthermore, since the molten metal is naturally cooled for a while after pouring, the molten metal flows sufficiently to the tip of the mold during this time, and the molten metal flows particularly well into thin-walled areas. This also improves the yield, especially for thin-walled products.

[Brief explanation of drawings]

FIG. 1 is a plan view of an embodiment of a cooling device according to the present invention, FIG. 2 is a cross-sectional view taken along the line 2, FIG. 3 is a partially sectional side view, and FIG. 4 is a cross-sectional view of a mold. FIG. 5 is a partially enlarged view. 26... Water tank, 46... Pressure pump, 60
... Ceramic shell mold, 64 ... Sprue rod part,
66...product department, 68...runner, 70...drawing section.

Claims (1)

[Scope of Claims] 1. In an investment casting method using a tree-shaped ceramic shell mold, the mold 60
The runner 6 communicates the sprue rod part 64 and the product part 66.
The walls of mold 8 are thickened to increase heat capacity, a constricted part 70 facing the sprue rod part 64 is formed in this runner 68, and the entire mold 60 into which the molten metal is poured is naturally cooled for a while. By forcibly quenching from the outside, the entire portion of the hot water in the product part 66 that contacts the inner surface of the mold 60 is first solidified in a shell shape, and then the inside of the product part 66 and the constricted part 70 are solidified in sequence. Investment casting method. 2. The investment casting method according to claim 1, wherein the mold 60 is rapidly cooled by spraying pressurized water.